The following methods are generally known as intraocular tension measuring methods: a method of applying a predetermined pressure to a cornea and monitoring a depression of the cornea at this time, thereby measuring intraocular tension; and a method of, by making a presser in contact with the cornea or by blowing air to the cornea, measuring a tension when a portion of the cornea becomes flat, thereby measuring intraocular tension. With those methods, it is necessary to ensure high safety because the cornea is directly stimulated. Accordingly, it is required that an examiner is a doctor or a health professional. In addition, a load on a person when examined is large because local anesthesia is required or air blowing causes discomfort.
Regarding such problems, several kinds of methods were proposed: a method of vibrating the surface of an eyeball by a sound wave and measuring intraocular tension based on an amplitude of the vibration, a resonance frequency of the eyeball, or a velocity of a surface wave of the eyeball (JP 02-181241A, U.S. Pat. No. 5,375,595, and U.S. Pat. No. 5,251,627); a method of pressing down an eyelid in a closed-eye state to measure intraocular tension (JP 06-105811 A, JP 08-280630 A, and JP 08-322803 A); and the like.
On the other hand, in a method of measuring an intracranial pressure using a sound wave, a Q value is known as one of the parameters related to the intracranial pressure (U.S. Pat. No. 5,919,144).